The present invention relates to ink ejection apparatus, and more specifically it relates to such apparatus in which the discharged ink droplets are accelerated by a stream of air supplied from a pressurized air source which is energized during operation of the apparatus.
The air-accelerated ink ejection apparatus disclosed in U.S. Pat. No. 4,106,032 includes an ink ejecting unit having a liquid chamber to which ink is supplied from a liquid container and an air chamber provided forwardly of the liquid chamber and axially aligned discharge channels for discharging ink therethrough into the atmosphere when the pressure inside the liquid chamber is increased rapidly by means of a piezoelectric transducer mounted adjacent to the liquid chamber in response to electrical drive signals applied thereto. The air chamber is constantly supplied with pressurized air from a pressure source when the apparatus is in operation to provide a stream of air that accelerates the discharged ink droplets onto a writing surface. The pressurized air is also supplied to the liquid container so that there is established a static balance between the pressures in the air and liquid chambers. This results in lowering of the minimum operating voltage of the apparatus and ensures that the reproduced image has a minutely changing gradation.
However, when the air supply source is energized or de-energized simultaneously with the starting and stopping of the apparatus, the static pressure balance is momentarily lost due to the fact that the pressures in the air and liquid chambers do not vary at the same rate. This results in the ink emerging spontaneously to the outside or results in the air being forced into the liquid chamber causing an ink backflow. The latter is a more serious problem than the former since it often results in a complete failure of ink ejection thereafter even in the presence of electrical signals applied to the piezoelectric transducer. Similar problems could occur when the air supply source is de-energized.